The present invention relates to a process for the preparation of milk concentrates and milk powders having a long storage life utilizing techniques which are known per se.
By bringing milk into a concentrated form or into a powder form and subjecting it to one or more heat treatments and to an aseptic packaging method, not only its storage life is prolonged but also the cost of transport is limited. For use, the concentrated or powdered milk product can be recombined or reconstituted.
In the case where in particular unsaturated fatty acid-containing compounds are present, however, the process of fat decay or `turning rancid` develops relatively easily and rapidly with milk concentrates and milk powders. This process of turning rancid gives rise to deteriation of the taste and problems of uptake and easily leads to problems of indigestion, in particular in sensitive individuals. More particularly, this problem occurs with milk products which have been enriched with unsaturated fatty acid derivatives or in which the milk fat has been replaced completely with these derivatives. Examples of such unsaturated fatty acid derivatives include fats, phospholipids or emulsifiers which contain a high percentage of unsaturated fatty acids and/or strongly unsaturated fatty acids. Enrichment of milk and milk powders with unsaturated fatty acid-containing phospholipids or emulsifiers is done for technological or physiological reasons.
An important reason for enriching milk or milk powders with fats containing a high percentage of unsaturated fatty acids or strongly unsaturated fatty acids is to prevent or reduce cardiovascular diseases, atopies, rheumatic disorders or diabetes. In particular, such products contain a high percentage of oleic acid, linoleic acid which may or may not be conjugated, .alpha.-linolenic acid and unsaturated C.sub.20 and C.sub.22 fatty acids.
Thus, to prepare food for premature children the fat fraction of milk concentrates or milk powders is enriched with strongly unsaturated fatty acids of the type C.sub.20 .omega.-6 and C.sub.22 .omega.-6+C.sub.20 .omega.-3 and C.sub.22 .omega.-3. These fatty acids are typically denoted by the name of LC-PUFAS, which is an abbreviation of "Long Chain poly-Unsaturated Fatty Acids". Examples of LC-PUFAS include: C.sub.18 :3.omega.6 (.gamma.-linolenic acid; GLA), C.sub.20 :3.omega.6 (dihomo-.gamma.-linolenic acid), C.sub.20 :4.omega.6 (arachidonic acid; AA), C.sub.18 :4.omega.3 (octadecatetraenoic acid), C.sub.20 :5.omega.3 (eicosapentaenoic acid; EPA), C.sub.22 :6.omega.3 (docosahexaenoic acid; DHA or DCHA).
LC-PUFAS are preferably included in the fat fraction of food for premature children together with the biochemical precursors C.sub.18 :2.omega.6 (linoleic acid) and C.sub.18 :3.omega.3 (.alpha.-linolenic acid). The reason for this is that the biochemical conversion of the precursors by desaturase and elongase enzymes proceeds only suboptimally in premature infants. LC-PUFAS, such as GLA, AA, EPA and DHA, are incorporated in particular in the fat fraction of food for premature infants because these fatty acids are of importance for optimum structuring of the cell membranes.
Biochemical conversions may also proceed suboptimally in non-premature infants. This is in particular a medically recognized problem with the conversion of linoleic acid to .gamma.-linolenic acid (GLA) in elderly people. The fat fraction of milk or milk powders is then enriched with unsaturated fatty acids of the type GLA.
From the prior art, for instance European patent application 0 404 058, it is known to avoid the problem of unsaturated fatty acid-containing products turning rancid by adding to them antioxidants, such as .alpha.-tocopherol, optionally together with an emulsifier, such as lecithin, and/or by gassing these products with, for instance, nitrogen gas and/or carbonic acid gas and subsequently storing them under this inert gas.